‘We were in a secret cathedral’ … the 1996 Glyndebourne production of Theodora, featuring Dawn Upshaw as Theodora and David Daniels as Didymus. Photograph: Mike Hoban

Peter Sellars, director

I had heard Lorraine Hunt singing Theodora in a concert performance, and was overwhelmed by the drama and sheer beauty of Handel's music. The story is basic tabloid fare, and Handel treats it almost entirely as interior drama. [An oratorio in three acts, it concerns the Christian martyrdom of Theodora and her Roman lover Didymus.] When Glyndebourne asked me where they should begin with staging Handel, it was easy. At that time, people didn't quite know what Theodora was: we were in a secret cathedral, discovering a masterpiece the world did not know.

The staging flowed in an extremely organic way. Visionary works such as this wait for another era in which they are allowed to speak in their own language and not have to ventriloquise the conventional wisdom of the day. A lot of it was done as in medieval or byzantine art – as simply as possible: the emotional and spiritual aura of each character was what we were concerned with.

The work is a soundtrack for two people leaving this world that is as chilling as anything Handel ever wrote. A lot of opera focuses on execution. It's a huge question: when we take people's lives as a society; when and how we justify killing. In the US, execution had been illegal for a period and then [in 1976] the Supreme Court decision turned it around. It was decided that lethal injection was "humane", but it was hidden away. I thought it was important to see what the process was. We investigated and were incredibly literal, down to the timing.

The effect was profound. During most performances, people had to be carried from the auditorium; there were emergency medical services standing by. I am not proud of putting people into an emergency medical van, of course, but I do think that's why the Greeks invented theatre: to put these things in front of citizens and say, how do we feel about them?

There was an incredible rehearsal where we ran the first act for the first time in the darkened theatre, and the piece just rose up, like some majestic host and said, "I'm here." We were weeping, holding each other, truly overwhelmed. The production remains a high point of all our lives.

Glyndebourne's general manager had asked if there was a Handel piece I would like to do. They had never staged anything of his there before. I wanted an oratorio, something that would use Glyndebourne's chorus, rather than an opera – and Theodora had stuck in my mind as incredibly moving. He said: "That's curious, the fellow we've asked to direct said the exact same thing!"

I had not met Peter before although of course I knew of him: he's a fellow of great notoriety, in the best sense of the word. You knew that he wasn't going to give you anything other than a controversial, or at least a very personal, sense of the drama. The fact that this Christian woman and her converted lover find themselves on a gurney in a Texas military hospital awaiting execution was incredibly shocking, but I found it horribly moving. We were talking about martyrdom, a word that's existed as long as humans have. Peter was hellbent on making a political statement, registering his dismay and revulsion about aspects of America, but also making music that was written several hundreds of years ago more relevant.

The starting point of any successful lyric piece is giving the singers a long leash. I gave space to them as well as to the music. We had so many happy moments in the casting. I wanted desperately to have Lorraine Hunt: the role of [Theodora's friend] Irene is strong and forthright, as Lorraine was as a singer and a human being. Richard Croft [as Didymus's friend Septimus] was also someone I particularly wanted; there is great honesty in the way he sings.

It's an incredibly emotional piece. We were all caught up in it. I remember Lorraine not being able to mark in rehearsals [sing in a way that rested her voice]. She'd be singing full voice at 11am.